A semiconductor device is known which includes a resin package sealing two semiconductor elements and has metal plates exposed at both surfaces of the resin package as heat diffusing plates. The metal plates are electrically connected to electrodes of the semiconductor elements in the resin package. That is, the metal plates serve as beat diffusing plates as well as electrodes. Such a semiconductor device is described in, for example, Japanese Patent Application Publications No. 2015-170810 and No. 2012-235081. Each of semiconductor elements includes electrodes on both surfaces thereof. Each of the semiconductor elements is interposed between a pair of metal plates, and the metal plates in the pair are respectively bonded to the corresponding electrodes via soldered portions. It should be noted that “an electrode and a metal plate are bonded via a soldered portion” herein includes a case where the electrode and a spacer are bonded via a soldered portion, and the metal plate is bonded to that spacer via another soldered portion on an opposite side with respect to the spacer. The two semiconductor elements are sealed in a resin package. Each pair of the metal plates has a surface of one of the metal plates exposed from the resin package, and this surface serves as a heat diffusing plate. For the sake of simplifying the explanation, the two semiconductor elements will be termed a first semiconductor element and a second semiconductor element, respectively. The pair of metal plates interposing the first semiconductor element therebetween will be termed first and second metal plates, and the pair of metal plates interposing the second semiconductor element therebetween will be termed third and fourth metal plates. The first and third metal plates are exposed at one surface of the resin package, and the second and fourth metal plates are exposed at an opposite surface to the one surface of the resin package. To electrically connect the two semiconductor elements, a first joint is provided at an edge of the first metal plate, a second joint is provided at an edge of the fourth metal plate which is exposed from the resin package on the opposite side to where the first metal plate is exposed, and these joints are bonded by a soldered portion inside the resin package.